The miridon, a massive, green and reptilian sea monster, was indigenous to the oceans surrounding Tarnoonga. It commonly built nests and swam around the numerous undersea mountain summits that protruded from the water.
In the year 15 BBY, the pirate Captain Gir Kybo Ren-Cha utilized one of these mountain peaks as his base of operations. A favored pastime of his involved compelling captives to walk the plank of his desert skiffs, then observing their descent into the water below–a meal for the miridon. Kybo was under the false impression that he had tamed the beast and that it would obey his orders, but this was simply a figment of Kybo's imagination.
During one particular event, Kybo's crew threw Jann Tosh along with the droids, C-3PO and R2-D2, into the deep ocean hoping to witness the miridon consume them. Nevertheless, owing to R2's dome propeller attachment, they managed to evade being eaten and effectively confined the creature within the wreckage of a submerged freighter.
Ultimately, the miridon broke free from its confinement and made its way back to Captain Kybo's pirate hideout, seeking additional food–specifically the bipedal variety.